The rapid growth in popularity in recent years of bicycling and hiking has resulted in the development of numerous accessories in the form of backpacks and knapsacks. While the known forms of these devices are in many cases admirably suited for their intended purposes when fully packed, the empty pack is often rather bulky and inconvenient to carry. For example, if the uses wishes to hike or bicycle to a particular place to pick up supplies, the pack must be carried along until it is needed. Or, if the pack is used to carry sports equipment such as a tennis racquet and balls, it is inconvenient to have to contend with a bulky object which must be left beside the playing area after it has been emptied. Often, the user on a bicycle must be encumbered with the empty pack on his or her back, particularly since most prior art packs are not convertible for safe attachment to a bicycle. Even the hiker has to carry the pack with its bulky assemblage of straps, flaps and so forth. Thus, a need exists for a backpack or knapsack which is compact and lightweight and which includes some provision for easily collapsing the empty pack into a configuration easy to store and carry.